The short answer
4 × 6 inches is the size most people mean by a standard postcard, and it mails at the USPS postcard price. That price applies only to rectangular cards from 3.5 × 5 to 4.25 × 6 inches and 0.007–0.016 inch thick. Larger cards such as 5 × 7, 5.5 × 8.5, 6 × 9, and 6 × 11 inches need letter postage when you mail them with stamps, and a card over 6⅛ inches high or 11½ inches long is charged as a large envelope (flat).
Common postcard dimensions
Six sizes cover most printed postcards in the US. The table gives each in inches and millimeters, plus the pixel count a design needs at 300 pixels per inch before any bleed is added. Conversions use the exact definition of the inch, 25.4 millimeters.
The aspect ratio is the long side divided by the short side. It matters for two reasons: USPS treats letter-size mail with a ratio below 1.3 or above 2.5 as nonmachinable, and artwork made at one ratio loses part of the design when it is cropped to another.
| Size in inches | Millimeters | Pixels at 300 ppi | Aspect ratio |
|---|---|---|---|
| 4 × 6 | 101.6 × 152.4 | 1200 × 1800 | 1.50 |
| 4.25 × 5.5 | 108.0 × 139.7 | 1275 × 1650 | 1.29 |
| 5 × 7 | 127.0 × 177.8 | 1500 × 2100 | 1.40 |
| 5.5 × 8.5 | 139.7 × 215.9 | 1650 × 2550 | 1.55 |
| 6 × 9 | 152.4 × 228.6 | 1800 × 2700 | 1.50 |
| 6 × 11 | 152.4 × 279.4 | 1800 × 3300 | 1.83 |
Is 4 × 6 a postcard size?
Yes. 4 × 6 inches is the size most people mean by a standard postcard, and it fits inside the USPS postcard-price window of 3.5 × 5 to 4.25 × 6 inches. The quarter-sheet 4.25 × 5.5 card, cut four to a sheet of letter paper, fits too.
Are most postcards 4 × 6 or 5 × 7? For mailing, the difference that matters is price: a 4 × 6 card mails with the $0.65 postcard stamp, while a 5 × 7 card is too tall and too long for the postcard price and needs a $0.82 letter stamp. Both are USPS retail prices effective July 12, 2026, unchanged in the October 4, 2026 Notice 123. The full postcard-stamp rules and price history are in our postcard stamp article.
What are USPS rules for postcards?
To mail at the postcard price with a stamp, Domestic Mail Manual 101 requires each card to be:
A card that doesn’t meet these standards must not carry the word “Postcard”. Anything marked “Postcard” or “Double Postcard” has to travel First-Class Mail, Priority Mail, or Priority Mail Express.
- Rectangular, at least 3.5 inches high, 5 inches long, and 0.007 inch thick.
- No more than 4.25 inches high, 6 inches long, and 0.016 inch thick, and no more than 3.5 ounces.
- Made of unfolded, uncreased paper or cardstock of uniform thickness, about the quality of a USPS stamped card.
- Free of attachments other than paper labels or seals fixed with permanent adhesive.
- Addressed on the side that carries the postage. Length is the side parallel to the address.
Which postcard sizes mail at postcard, letter, or flat prices
Size, thickness, and shape decide the price. A card outside the postcard limits is charged as a letter, which can be up to 6⅛ × 11½ inches and ¼ inch thick. A letter-size card more than 4.25 inches high or 6 inches long should be at least 0.009 inch thick, and one that is thinner, or has an aspect ratio under 1.3 or over 2.5, is nonmachinable and pays a $0.49 surcharge. Cards mailed at the postcard price don’t pay that surcharge, so a 4.25 × 5.5 card is fine with a postcard stamp.
Businesses mailing presorted commercial First-Class Mail get a wider card window: up to 6 × 9 inches at card prices, at least 0.009 inch thick for cards larger than 4.25 × 6, with the 5.5 × 4.25 quarter-sheet card allowed as an exception to the 1.3 minimum ratio. USPS Marketing Mail has no separate postcard price at all.
| Card size | Stamped price | Commercial First-Class card price? | Why |
|---|---|---|---|
| 4 × 6 | Postcard, $0.65 | Yes | Within 4.25 × 6 inches |
| 4.25 × 5.5 | Postcard, $0.65 | Yes, as the quarter-sheet exception | Within 4.25 × 6 inches |
| 5 × 7 | Letter, from $0.82 | Yes | Taller and longer than the postcard limit |
| 5.5 × 8.5 | Letter, from $0.82 | Yes | Taller and longer than the postcard limit |
| 6 × 9 | Letter, from $0.82 | Yes, at the maximum | Taller and longer than the postcard limit |
| 6 × 11 | Letter, from $0.82 | No | Longer than 9 inches |
| Over 6⅛ inches high or 11½ inches long | Large envelope, from $1.69 | No | Larger than letter size |
Is a postcard A5 or A6?
A6. ISO 216 defines A6 as 105 × 148 millimeters, about 4.13 × 5.83 inches, which falls inside the USPS postcard-price limits. Compared with a 4 × 6 card, A6 is about 3 millimeters longer on the short side and about 4 millimeters shorter on the long side, so artwork made for one needs a small crop to fit the other.
A5 is 148 × 210 millimeters, about 5.83 × 8.27 inches. That is too big for the postcard stamp, so an A5 card mails at the letter price in the US, close to a 5.5 × 8.5 card.
Bleed, safe area, and resolution
In IRIS’s 4 × 6 and 6 × 9 print files, the artwork runs 0.125 inch past each edge of the finished card. That margin, called bleed, is trimmed away so the image reaches the edge without a white sliver. The safe area is the inner zone where IRIS keeps the title and greeting, clear of the trim. IRIS renders the front at 300 pixels per inch:
| IRIS size | Print file size | Front image pixels | Text kept at least this far from the file edge |
|---|---|---|---|
| 4 × 6 | 6.25 × 4.25 inches (0.125-inch bleed on each side) | 1875 × 1275 | 0.25 inch |
| 6 × 9 | 9.25 × 6.25 inches (0.125-inch bleed on each side) | 2775 × 1875 | 0.25 inch |
| Small 5.5 × 4.25 | 5.5 × 4.25 inches | 1650 × 1275 | 0.25 inch |
| Pro 8.5 × 5.5 | 8.5 × 5.5 inches | 2550 × 1650 | 0.3125 inch |
Preparing a design for an IRIS postcard
An upload doesn’t need crop marks or a bleed you measured yourself. IRIS takes a JPEG, PNG, or WebP image up to 15 MB as the front artwork, crops it to the size you pick, and generates the print PDFs. Export at high resolution without crop marks or printer guides, use RGB color, and keep important details away from the outer edges.
Because the editor crops to the chosen proportion, a design made for 5 × 7 or A6 loses some material on a 4 × 6 card. Move the focal controls and check the front preview before checkout. You write the back message and addresses in the editor rather than uploading a back.
IRIS postcard sizes and prices
IRIS prints postcards in full color and mails them to US addresses by USPS First-Class Mail, with postage included in the price, so you don’t need to work out which USPS rate a size falls under. The editor shows the sizes available for your card when you create it. A sender name and return address plus a recipient name and address are required, and you review both sides, the address, and the total before paying.
IRIS mails individual postcards. It doesn’t run mailing-list campaigns or Every Door Direct Mail, schedule future mailings, or mail outside the US, and it can’t guarantee a delivery date.
| Size | Price |
|---|---|
| 4 × 6 inches | $3.49 |
| Small 5.5 × 4.25 inches | $3.49 |
| 6 × 9 inches | $4.49 |
| Pro 8.5 × 5.5 inches | $4.49 |
Sources & further reading
Product details checked against the IRIS API contract when this article was published. Platform references can change; consult the linked documentation when implementing.
- USPS Domestic Mail Manual 101, Physical Standards (6.2 Cards claimed at card prices)
- USPS Domestic Mail Manual 201, Physical Standards for commercial letters and cards
- USPS Quick Service Guide 201, Physical Standards for Commercial Letters and Postcards
- USPS Domestic Mail Manual 133, First-Class Mail prices and eligibility (nonmachinable surcharge)
- USPS Notice 123, Price List (Postal Explorer)
- USPS, First-Class Mail
- USPS Postal Explorer, Business Mail 101: Sizes for Postcards
- ISO 216:2007, Writing paper and certain classes of printed matter — Trimmed sizes
- NIST Office of Weights and Measures, SI units of length
Published by IRIS Postal Forms, operated by Great Lakes Computing Office LLC. Send a correction.